The present invention relates to prefabricated electric ducting adaptable for several rated currents for distributing low power, of the type comprising:
a metal protective casing in the form of a tubular conduit with an approximately parallelepipedic section,
a flat support which extends longitudinally inside the casing and which is a shaped piece made by extrusion from an electrically insulating plastic material and is formed by a base plate on which are mounted two outer ribs at right angles with the base plate and, at even spacings parallel to the outer ribs, several inner ribs, these outer and inner ribs extending longitudinally over the whole length of the base plate and being shaped so as to define therebetween and with the base plate several parallel longitudinal grooves of the same C shaped section with straight edges, in each of which a current conducting bar is housed flat, this flat support having its base plate engaged against the bottom of the casing,
taps spaced evenly apart over the length of the casing, each tap being provided with orifices situated opposite the conducting bars for the passage of removable current tapping members, each of the tapping members being adapted for providing an electric contact with a corresponding conducting bar.
Such an electric ducting with conductors in the form of bars disposed flat in a flat insulating grooved support is at present used for the distribution of low powers, which are usually defined as corresponding to rated ducting currents between 40 and 125 amps, the most widely used current ratings being 40A, 63A and 100A.
For supplying low power appliances, the conducting bars housed in the grooves of the insulating support of the ducting of the prior art are flat shaped pieces of rectangular shape, the section of the bars forming the phase conductors varying as a function of the rating of the ducting. Now, when it is desired to use the same flat grooved support obtained by extrusion for all the ratings of the ducting, it proves that the variations of section of the rectangular conducting bars are too great from one rating to another providing, in particular for the low ratings, a good mechanical strength of the bars when positioning them in the grooves of the support. It should also be noted that the rectangular conducting bars are usually made from copper for the above indicated ratings, which increases the cost price of the prefabricated ducting.
Furthermore, the fact of having very thick rectangular conducting bars in the grooves of the insulating support, for a given section of said bars, reduces the heat exchange surface between the bars and the external casing of the ducting, which does not allow good heat dissipation from the conducting bars.
It is an object of the present invention to overcome these drawbacks and to provide prefabricated electric ducting for low power distribution systems, which is easily adaptable to several current ratings by using particularly well shaped and dimensioned conducting bars so as to keep the same size for each of the current ratings and increase the heat exchanges.
It is another object of the invention to provide high thermal conductivity of the prefabricated ducting, for all current ratings.